JP4347217B2 - Piston body manufactured by powder metallurgy with a support abdomen and method for manufacturing the same - Google Patents

Abstract

The piston has a one-part body (6) with a peripheral projecting web (12) next to an end face. Parallel support webs extend from the peripheral web to the other piston end face. At least some of the support webs have a cross groove, and every two neighboring webs define a groove-shaped aperture with an open end facing away from the projecting web. A collar-like seal (9) of heat-deformable sealing material is formed on the piston body, so that all webs are at least partially formed in the collar material. The piston with integral is produced from a green compact, which is pressed from a sinterable metallurgic powder in a first stage. In a second stage, the green compact is sintered to form a blank (6.1), and this is finished by cold forming and pressing with calibrating tools

Description

  A known shock absorber piston according to Patent Document 1 has a piston body, and the piston body has a circumferential abdomen on its circumferential surface. A large number of abdominal parts extending in the axial direction are provided on one side of the circumferential abdomen. in the process of. A seal made of thermoplastic plastic is injected and applied to this piston body by injection molding, and the abdomen extending in the axial direction is between them, and the groove is completely filled with the seal material. Useful for locking and piston guidance. Seals applied in injection molding allow narrow tolerances to prevent so-called “blow-by” and thus cause a positive sealing of the associated cylinder chambers. Methods for producing such injection molded seals are relatively expensive.

  Patent Document 2 discloses a known piston / cylinder device having a piston body having a large number of circumferential grooves on its peripheral surface. A bowl-shaped preform made of PTFE (polytetrafluoroethylene) is provided for applying the seal, and this preform is first loosely placed on the piston body. The piston body thus prepared is then first pushed into a molding and sizing cylinder heated to a high temperature, and the PTFE material is pushed into the groove on the circumferential surface of the piston body under the influence of heat. The piston body is subsequently cooled in a correspondingly formed cooling cylinder with a crimped seal. The groove is completely filled with sealing material, thus providing a shape-fitting fixed connection between the seal and the piston body peripheral surface. In order to be used as a shock absorber piston, it is still necessary to remove the bottom of the preform that covers the front of the piston body on one side.

  The known shock absorber piston according to US Pat. No. 6,056,089 is only substantially different from the above method in that a stamped annular plate is used instead of a bowl-shaped preform for its seal application. Absent. This annular plate is attached to one end of the piston body. The piston body prepared in this way is also pushed into a heated molding and sizing cylinder, and the annular plate is wound around the circumferential surface of the piston body as a strip, and subsequently heated in a groove extending in the circumferential direction of the piston body. Pushed under the influence of. Subsequently, the piston with the crimped seal is passed through the cooling tube. In this case, the sealing material substantially completely fills the groove, and the seal is fixedly connected to the peripheral surface of the piston body in a shape fitting manner.

  Both of the above methods may require a considerable pressing pressure for the molding of the sealing material and the complete pushing into the groove on the circumferential surface of the piston body, and the sealing material forming the seal is subjected to strong deformation, It has the disadvantage of adversely affecting the structure of the sealing material.

  Patent Document 4 discloses a piston for a piston / cylinder device, in particular, a shock absorber piston, has a piston body, and the piston body protrudes from the circumferential surface in a region adjacent to one piston end on the circumferential surface. It is provided with a peripheral abdomen, and this peripheral abdomen is followed by a longitudinally extending support abdomen extending in the direction of the other piston end and juxtaposed in parallel, and each two adjacent support abdomen are grooved The concavities are limited, and these concavities are open in the longitudinal direction at the end away from the peripheral abdomen, and a cuff-like seal made of a hot-moldable seal material is on the piston body, and the peripheral abdomen is also supported Is formed so as to be integrally formed in the sealing material only over a part of the height.

  This known solution has shown that the seal need not be in close contact with the piston body all around in order to provide a good seal between the piston cuff seal on the one hand and the outer contour of the piston body on the other hand. . For a series of use cases, it is sufficient for the sealing cuff to simply abut against a relatively narrow circumferential abdomen in the circumferential direction. Surprisingly, it turns out that it is not necessary to completely fill the groove-like recesses between the longitudinally extending support bellows with the sealing material in order to ensure a secure and secure connection between the seal and the piston body. did. At the same time, there remains enough free space for the sealing material to escape when it expands as a result of the temperature rise, and the piston is guided without problems through the longitudinally extending support belly.

If only one peripheral abdomen protruding from the peripheral surface for fixing the cuff-like seal is disposed, it may not be sufficient depending on the situation, and it is desirable to dispose two peripheral abdomen on each end side. Are coupled by vertically extending support abdomen spaced apart from each other in parallel. However, manufacturing such a piston body by a powder metallurgy method by pressing a green compact made of a sinterable metal powder and subsequently sintering causes considerable molding technology problems. Has been proposed to be divided into two partial bodies. Each of the partial main bodies has one peripheral abdomen at one end, and longitudinally extending support abdomen spaced from each other start from this peripheral abdomen. Both partial bodies can each be formed from a sinterable metal powder into a green compact and then sintered without great difficulty. The complete piston is in this case assembled from both finish-sintered parts such that a circumferential belly is arranged at the piston end away from the dividing plane. It is then possible to provide additional lateral grooves by tilting the support belly at the end closer to the dividing plane. The disadvantage of this concept lies in the time-consuming assembly of both partial bodies when both partial bodies have to be assembled in a limited relationship with each other. This corresponds to the case of a piston body for a shock absorber piston, for example. This is because the partial passages present in both partial bodies must then be aligned exactly.
European Patent Application No. 0658611 US Pat. No. 3,212,411 European Patent Application Publication No. 682190 German Patent Application Publication No. 1847342 German Patent Application Publication No. 10108246

  The object of the present invention is to provide a piston, in particular a shock absorber piston, which can be easily manufactured.

  This object is achieved according to the invention by an integral piston body having the features of claim 1.

  A method for producing a piston body according to the invention is specified in claim 3.

  Other features of the invention are set out in the following description of the embodiments and in the dependent claims.

  The invention is explained in detail on the basis of a schematic drawing of an embodiment.

  The shock absorber shown in FIG. 1 as a functional diagram in an axial sectional view couples two relatively movable members such as an axle and a vehicle frame. The shock absorber has a cylinder part 1 which is connected to one of both relatively movable members. A piston 2 guided in the cylinder 1 is fixed to a piston rod 3, and the piston rod has its free end fixed to the other member of both of the relatively movable members. The cylinder 1 is then sealed on both sides and filled with hydraulic fluid, the piston / cylinder device is designed to be double-acting, and the piston separates the two cylinder chambers 4, 5 from each other.

  The piston body 6 of the piston 2 has a plurality of through passages 7 and 8 that extend side by side. The outlets 7 and 8 are covered with a throttle valve 7.1 or 8.1, respectively, on the outlet side, which is still explained in terms of function. At that time, the arrangement is made such that a plurality of through passages 7 and a plurality of through passages 8 are alternately arranged around the cylinder axis.

  The peripheral surface of the piston 2 is provided with a cuff-like seal 9, which seals the cylinder chamber 4 against the cylinder chamber 5. When the piston 2 moves into the cylinder chamber 4, the liquid is pressurized through the through passage 7 against the restoring force of the throttle valve 7.1. The through-passage 8 is then closed and held by the pressure of the liquid chamber 4 applied to the throttle valve 8.1. When moving in the reverse direction, the through passage 7 is closed by the throttle valve 7.1, while the liquid can flow back from the cylinder chamber 5 to the cylinder chamber 4 through the through passage 8.

  By the way, when such a piston body is reciprocated as described above and the load is high, the cuff-like seal 9 is correspondingly loaded also during the return movement. It is no longer sufficient to securely fix the cuff-like seal against axial loads. By the way, in order to be able to manufacture such a piston body in an integrated manner so that an additional lateral groove for fixing the cuff-like seal is provided, first, a green compact is obtained from a sinterable metal powder. Pressed in the shape shown in FIG. 2 and described in more detail below, followed by finish sintering to blank 6.1.

The blank 6.1 is provided with a large number of support abdominal portions 10 on its peripheral surface, each supporting abdominal portion defining a corresponding groove-like recess 11, and the front surface 4.1 to the front surface 5. 1 extends to the other end of the blank 6.1 in the vicinity. The circumferential abdomen 12 and the support abdomen 10 forming the outer surface of the piston body 6 are at the same level. The outer surface is hatched for ease of viewing. The support belly 10 and correspondingly the groove-like recess 11 extend parallel to the axis.

FIG. 3 shows the piston body 6 in a horizontal section along the line III-III in FIG. 2, and the structure of the support abdomen 10 and the groove-like recess 11 can be recognized.

  In FIG. 4, the piston body 6 is partly shown in a sectional view and in a side view in its final shape after the seal 9 is omitted and a transverse groove 11.1 is provided on the surface of the longitudinal abdomen 10. The transverse grooves 11.1 are provided in the sintered blank 6.1 by the coining method, as will be explained further below, and the blank is then still sized by the coining method. A seal 9 is then applied to the finished sized piston body 6.

  The cuff-like seal 9 disposed on the peripheral surface of the piston body 6 is made of hot-moldable plastic, mainly PTFE. In the embodiment shown here, a cuff-like seal 9 is formed on the piston body 6 by hot forming.

At the time of hot forming of a sealing material that can be constituted by a prefabricated annular plate or a prefabricated tube member, the support abdomen 10 and the peripheral abdomen 12 are included in the material of the cuff-like seal 9 only over a part of the height. It is integrally formed, and a certain free space still remains between the material of the seal 9 and the bottom of the groove-shaped recess 11 , and the seal material flows freely and without force into the groove- shaped recess 11 when the seal 9 is formed. Can do. During this molding process, the cylindrical outer surface 13 of the seal 9 is simultaneously sized so that the required tolerances for the inner diameter of the cylinder 1 can be kept. Especially when such a piston / cylinder device is used as a shock absorber, the entire system will be heated during operation, and this free space remaining at the bottom of the groove allows the sealing material to expand into the groove within a certain limit. The seal wear is reduced at the cylindrical peripheral surface adjacent to the edge of the seal 9. The piston 2 is supported throughout its height virtually without tilting. The seal 9 is supported by one groove end on the inner surface of the circumferential abdomen 12.

In FIG. 5, the positioning of the seal 9 is significantly enlarged and shown in a partial sectional view corresponding to FIG. The seal 9 is in this case made of a homogeneous material, which is partly formed integrally in the groove-like recess 11 and the transverse groove 11.1 during the hot forming, while on the other hand the support belly 10 and the peripheral belly 12 Are correspondingly formed integrally in the material. For clarity, with the cross-hatching in material formed integrally in the groove-like recess 11, groove-like recess 11 is in the fully made clear that they are not filled.

At that time, in order to prevent the material of the seal 9 from being overloaded in the groove-shaped recess 11 in the transition region B to the circumferential abdomen 12 during hot forming, the depth of the groove-shaped recess 11 is set in this region It decreases in the direction of the peripheral abdomen 12, that is, it decreases. This reduction in the axial support surface for the sealing material of the circumferential abdomen 12 is compensated by an additional support surface acting in the axial direction of the transverse groove 11.1 and in this region which receives high loads during subsequent operation. The advantage is that the material is subjected to a slight load on its structure by hot forming and thus has a higher stability.

  The method according to the present invention for manufacturing the piston body having the shape shown in FIG. 4 will be described in detail with reference to FIGS. First, in the first step, the green compact is pressed from the sinterable metallurgical powder as shown in FIG. 2, and after blank 6.1 is finish-sintered, as shown in FIG. 6, blank 6.1a Each blank 6.1a is taken out from the stockpile S1 and supplied to a press apparatus P having a first press part I and a second press part II.

  In addition to the normal upper punch 15.1 and the lower punch 16, the first press part I includes a coining die 14 guided in the radial direction, and through a coining die as will be described in more detail below. A transverse groove 11.1 is provided in the support abdomen 10.

  The blank 6.1b provided with transverse grooves in the press part I in the preceding coining step is then fed to the second press part II, where the blank 6.1b prepared in this way is also circumferential with respect to the piston end face. The outer peripheral surfaces of the abdomen and the support abdomen are also sized according to the completed piston body 6. This process is shown in FIG.

  In the press part II, the lower punch 16.2 is attached to the movable upper punch 15.2, and the shape surface of the lower punch coincides with the shape surface of the blank 6.1a or 6.1b to be inserted. In the first press part I, the blank 6.1a is practically only held by the movable punch 15.1 and the fixed counterpart punch 16.1, while in the second press part II, the pressure punch 15.2 is pressurized. Is added, and final molding for sizing the blank 6.1b to be inserted is performed, and the finished piston body 6 is formed.

  As shown in FIG. 8, the pressure punch 15 continues to be pulled back and protrudes in both press sections through the tool 17 and now the blank 6.1b with transverse grooves and the finished sized piston body 6 protrude from the press mold. The blank 6.1b can then be transported to the press section II, and the finished piston body 6 can be lowered to the warehouse S2, from which the finished piston body is then taken out for wearing the cuff-like seal 9.

  FIG. 9 shows the arrangement with the inserted blank 6.1a in a vertical sectional view of the first press part I. FIG. The upper punch 15.1 that has entered is not shown in this case. The coining die 14 is pushed into the material of the support abdomen 10 to form a transverse groove 11.1. This can be read from the enlarged view of FIG.

  The coining die 14 that can be fed in the radial direction has a slider shape, and can be fed toward the blank 6.1a in the radial direction, as is apparent from FIGS. 6, 7, 10, and 11. . In the illustrated embodiment, three coining dies 14 are provided and arranged at the same angular distance from each other. Depending on the dimensions, four or more coining die arrangements can be provided. An arrangement of coining dies facing just on two diameters is also basically possible.

As will be apparent from the enlarged view of FIG. 10, each coining die 14 has two parallel cutting edge coining ridges 18 for providing two transverse grooves 11.1 on the support belly 10 of the blank 6.1. When the pressure of the coining die 14 is applied, the coining ridge removes the material as shown in FIG. 7 under the cold forming of the sintered material, and the lateral groove 11.1 is formed. As can be seen from FIG. 10, this cold forming is performed only over a portion of the overall height of the support belly 10, resulting in a transverse groove 11.1 having a depth smaller than the groove-like recess 11 .

  The forming and sizing process can also be carried out with just one press part, the structure of which corresponds substantially to the press part I. However, the upper punch and the lower punch are configured in accordance with the upper punch 15.2 and the lower punch 16.2. Accordingly, in the first step, the blank 6.1a is only fixed by the upper punch and the lower punch, and the transverse groove 11.1 can be provided. Subsequently, the coining die 14 is pulled back, the pressure on the upper punch and the lower punch is increased, the blank is sized, and is then taken out from the mold as a finished piston body only.

It is an axial direction fragmentary sectional view of the piston and cylinder device for shock absorbers. It is a side view which shows the blank for shock absorbers by which sintering was carried out in a partial cross section. FIG. 3 is a schematic horizontal cross-sectional view of the blank along the line III-III in FIG. 2 with the sealing cuff removed. It is a side view which shows the piston main body by which finish molding was carried out, and the attached sealing cuffs by a partial cross section. FIG. 5 is an enlarged partial cross-sectional view of FIG. 4. Fig. 2 shows an apparatus for sizing a piston body blank with lateral grooves as a step of the manufacturing method. FIG. 7 shows the apparatus of FIG. 6 during a molding and sizing step. FIG. 7 shows the apparatus of FIG. 6 at the end of the forming and sizing step. FIG. 7 is a vertical cross-sectional view of the die forming portion of FIG. 6 with a blank inserted during the forming process. The configuration of the coining die is shown in an enlarged view. FIG. 10 is a plan view of the forming section of FIG. 9 having a coining die arrangement.

Claims (9)

A piston body for a piston / cylinder device manufactured by a powder metallurgy method, which has an integral piston body (6), and this piston body is adjacent to its peripheral surface and one piston end surface (4.1). In the region, a peripheral abdomen (12) protruding from the peripheral surface is provided, and on this peripheral abdomen, the support abdomen (10) extending to the other piston end surface (5.1) and spaced apart in parallel is arranged. ) And at least part of the support belly is provided with at least one transverse groove (11.1) between both piston end faces (4.1, 5.1), each with two adjacent supports The abdomen (10) defines groove-like recesses (11), and these recesses are cuffed of a sealing material that can be hot-molded, with the ends remote from the circumferential abdomen (12) open in the vertical direction. to Jo seal (9) is a piston body (6) on, 設腹portion (12) from moldable so integrally formed in the material of the cuff-like seal (9) over at least a portion of the support abdomen (10), the depth of the groove-like recess (11) is circumferential Piston body, characterized in that the region (B) adjacent to the abdomen (12) is smaller than the end surface (5.1) region away from the peripheral abdomen (12) . 2. Piston body according to claim 1 , characterized in that at least two transverse grooves (11.1) are provided. 3. Piston body according to claim 1 or 2 , characterized in that the transverse groove (11.1) has a smaller depth than the groove-like recess (11). A cuff-like seal (9) made of hot-moldable plastic is formed on the piston body by hot molding, the seal (9) does not completely fill the groove-like recess (11), and the lateral groove (11.1). The piston main body according to any one of claims 1 to 3 , wherein the piston main body is completely satisfied. A method for manufacturing an integrally piston body for a piston-cylinder device, the piston body is a circumferential surface, in a region adjacent to one of the piston end face (4.1), circumferentially projecting from the peripheral surface The abdomen (12) is provided, and this peripheral abdomen is followed by a supporting abdomen (10) that extends to the other piston end surface (5.1) and is juxtaposed in parallel, each having two adjacent The supporting abdomen (10) to define the groove-like recesses (11), and these recesses are open in the longitudinal direction at the end remote from the circumferential abdomen. In the first step, sinterable metallurgy From the powder, a green compact having a peripheral abdomen and a support abdomen is pressed, and in the second step, the green compact is finish-sintered into a blank (6.1), and in the third step a support abdomen (10 ) At least partially guided in the radial direction A cold groove is used to form the transverse groove (11.1) integrally with the coining die (14) while eliminating the material. In the fourth step, the blank (6.1) thus provided with the transverse groove (11.1) is formed. Is sized to its final shape by pressing with a sizing die. 6. The method according to claim 5 , characterized in that at least two coining dies (14) are used which are capable of pressing the blank in the radial direction, each coining die having at least one cutting edge coining edge. A pressing device (P) having at least two pressing parts (I, II) is used, and in the first pressing part (I), a blank (6.1a) is provided with a transverse groove (11.1) and at the same time a second press 7. A method according to claim 5 or 6 , characterized in that the blank (6.1b) with transverse grooves (11.1) in part (II) is sized. In the third step, the blank (6.1a) is effectively held only by the movable upper punch (15.1) and the fixed lower punch (16.1) to produce the transverse groove (11.1), transverse grooves (11.1), characterized in that provided in the support abdominal (10) over a small depth than the depth of the groove-like recess (11) by Koiningudai (14) which is guided in the radial direction, claim The method of any one of 5-7 . In the fourth step, the blank (6.1b) is a movable upper punch to which pressure is applied to the piston end surface (4.1; 5.1) and the outer peripheral surfaces of the peripheral abdomen (12) and the support abdomen (1). 15.2) and the fixed lower punch (16.2) and one that is sized by Koiningudai guided radially (14), characterized in that the entering the lateral groove (11.1), according to claim 5 9. The method according to any one of items 8 .

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